The bacterial ribosome has become one of the better understood cellular organelles composed of more than one kind of macromolecule. The interaction of a well defined particle and the soluble factors with which it interacts can now be studied in molecular detail. All of the components concerned in bacterial protein synthesis are known, an the empirical formula for the structure of the ribosome can be written. Pure ribosomal proteins, soluble factors and ribosomal RNA have been isolated and are being characterized in detail. Ribosomal particles and ribosome factor complexes can be assembled in vitro from purified components. These results are prerequisites for the proposed investigation which represents the application of the well established methodology of protein and RNA chemistry to the determination of ribosome structure and function. The goals of the project are: 1) identification of the active sites of the ribosome, in terms of the rbosomal protein comprising them, at which initiation factors and elongation factors bind to the particle; 2) establishment of an overall topography or map of the ribosome in which the location of each protein relative to neighboring proteins is determined; 3) determination of the binding sites on RNA for individual proteins and 4) the characterization and reassembly of subribosomal ribonucleoprotein fragments. The major experimental approach for the proposed research is the crosslinking with bifunctional reagents of neighboring proteins, either intraribosomal or between ribosome and soluble factor, or between protein and RNA; the subsequent isolation of dimers or oligomers and determination of the composition; and the sequence edetermination of protein bund RNA fragments. The results obtained and the methods employed will serve as a model for further studies on the structure and function of eucaryotic ribosomes. In a variety of systems from higher organisms there is increasing evidence to support the hypothesis that control at the ribosome level plays a vital role in cellular function development, differentiation and disease states including neoplasia.